The present invention relates to an inspection apparatus, an inspection method, and an inspection probe for a work (to be referred to as an electronic circuit board) having conductive patterns with narrow spacings, e.g., an electronic circuit having a pin grid array (PGA) structure or a multi-layered circuit board.
As the packing densities of electronic circuits such as ICs increase, the interconnections of electronic circuit boards are formed into highly integrated and multilevel metallization.
FIG. 1 shows a PGA package 100 as an electronic circuit board.
The PGA package 100 in FIG. 1 is at the stage before an LSI chip 105 mounted in the center of the package is bonded with lead wires. The LSI chip 105 is bonded to bonding pads (to be referred to as "BPs" hereinafter) 102 on a multi-layered ceramic board 104 with predetermined lead wires. As shown in FIG. 2, in the multi-layered ceramic board 104 of the PGA package 100, a given BP 102 is wired to a specific pin pad (to be referred to as a "PP" hereinafter) 101 through a lead wire 103. This lead wire 103 must not be short-circuited to another lead wire or have a discontinuity.
The inspection apparatus of the present invention is designed to check discontinuities and shorts in an electronic circuit board such as a PGA package like the one shown in FIGS. 1 and 2, especially in interconnections which are not seen from the outside.
In a PGA package (or LCC (Leadless Chip Carrier) package or the like), in particular, since the pitch of the BPs 102 is very small, it is difficult to specify a pad.
In a conventional inspection method and apparatus, a pair of connection pins for power supply and reception are brought into contact with electrodes to be inspected (e.g., the lands of a BP and a corresponding PP), and an electrical signal is supplied to one of the pins to inspect whether a predetermined signal is output from the electrode (or electrodes) for power reception. In order to reliably perform this inspection, an apparatus for accurately positioning pins on lands is required.
When the interconnection pitch of a circuit pattern is small, the pins can be easily and accurately positioned on lands. As the interconnection pitch decreases, the number of input/output points (measurement count) for a test increases, stricter positioning conditions are imposed on the test. For this reason, complicated, high-precision inspection jigs are required, resulting in an increase in cost.
In general, electronic circuit boards such as PGA packages respectively have different bonding pad patterns.
In a conventional method (e.g., disclosed in U.S. Pat. No. 4,035,722, which will be referred to as a "multi-probe method" for the sake of descriptive convenience), a high-precision probe head corresponding to the bonding pad and pin pad patterns of each PGA package is manufactured, and the head is brought into contact with the lands of the pin pads and the lands of the bonding pads at once to measure continuity between the lands. This multi-probe method allows a batch test of many pins with a high precision. However, a test head for a given board or package cannot be used for other boards or packages. Therefore, a head dedicated to each board or package is required, resulting in a high cost.
As an improvement on the multi-probe method, a moving probe method (e.g., U.S. Pat. No. 5,256,975) is known. In this method, one probe comes into contact with an electrode group (i.e., a pad group) to be inspected in units of lands.
The above multi-probe method and the moving probe method have their own advantages and disadvantages in terms of throughput including test speeds, the contact characteristics of probes, and costs. However, both the methods require high-precision positioning. High-precision positioning generally leads to structural or mechanical limitations. For example, the use of a probe head (multi-probe method) having contact pins with a small pitch makes it difficult to perform positioning with respect to a work. In the moving probe method, since positioning is performed in units of lands, it takes much time to perform an inspection.
In both the multi-probe method and the moving probe method, if the dimensional precision of a package to be inspected is high, positioning poses no serious problems.
However, in an IC package having a PGA structure, in particular, since the multi-layered ceramic board 104 undergoes a large change in dimension, the dimensions of the finished BPs 102 having a high wiring density inevitably vary. From the viewpoint of a work, positioning is very difficult to perform in a contact type inspection. That is, the errors between the head and the BP pattern are too large to perform an inspection by the multi-probe method. In the moving probe method as well, owing to the above variation, it is difficult to accurately position the probe pins.
Furthermore, in the moving probe method, the probe pins must be brought into contact with lands or patterns, resulting in undesired flaws.